The present invention relates generally to gangplanks for ships, and more particularly, is directed to an automatic, hydraulically controlled, extendable, safety gangplank which extends from the dock to the deck of a ship.
It is the usual practice for ocean going vessels to tie up to a dock when in port by securing numerous lines between the ship and the dock in well known manner. A gangplank is then extended between the surface of the dock and the deck of the ship to allow crew, passengers and workmen to travel back and forth between the ship and the dock with relative ease and safety.
Most prior art gangplanks were fairly elementary in design and structure and comprised essentially a sturdy walk-way of suitable length to extend between the dock and the deck of the ship. Usually, either permanent or semi-permanent type of handrails were affixed to the gangplank and extended upwardly sufficiently to provide lateral safety as personnel traversed the gangplank. The prior art gangplanks are generally hoisted into position by utilizing the ship board cranes for this duty and the ends of the gangplank were then secured both to the dock and to the ship in known manner to provide basic safety for the personnel using the gangplank.
In normal situations, the prior art gangplanks generally were suitable for the use and were designed to automatically adjust to natural conditions, such as the rise and fall of the tides, by assuming more or less angularity relative to the deck of the ship in response to the environmental changes. For most types of cargo ships and passenger ships, the gangplanks presently in use have proved to be generally satisfactory and have operated without problems for many years.
However, in the case of many types of vessels which vary greatly in weight between their loaded and unloaded conditions, for example, large tank type vessels, that is the giant supertankers that are currently being used in increased numbers, the prior art fixed length type of gangplank which is currently in use has proved to be highly deficient in providing a safe passage between deck and dock due to the very service of the vessel in question.
Specifically, the large tankers are designed to hold literally millions of gallons of liquid products and these vessels are designed for loading and unloading the liquid cargo in relatively short periods of time, for example twenty-four hours. Accordingly, in the case of unloading, a tanker can reach port and tie up to dock in heavily loaded condition wherein the deck of the ship is elevated only a relatively short distance above the fixed surface of the dock. Similarly, great changes in weight can occur when conventional freighters are loaded or unloaded. Under such conditions, when the gangplank is extended between the dock and the deck of a loaded ship, the angle between the gangplank walkway and the deck of the ship is relatively gentle and the ship's crew, visitors and other personnel experience no problem when traversing between the ship and the dock and the dock and the ship. However, while and after the vessel is unloaded, the ship will float higher in the water and the height between the surface of the deck and the dock will be drammatically increased. That is, in many such vessels, an increase in deck elevation as the vessel is unloaded of between twenty-five and thirty feet over a twenty-four hour period is commonplace.
Because of the increase of deck height relative to the fixed dock elevation, a gangplank that had originally been set at a gentle angle will then be steeply inclined in order to reach between the dock surface which is fixed and the elevated surface of the ship after the ship had been unloaded. Under such conditions, a prior art gangplank becomes quite different to traverse, especially when members of the crew and other users are loaded with packages, luggage, supplies, etc. This same relative change in elevation between the deck of the ship and the surface of the dock would also be present at the other end of the run, that is when an unloaded ship entered port to take on a load of petroleum or other liquid or dry products. In such an instance, the procedure would be exactly reversed, that is, initially the empty ship's deck would be elevated far above the surface of the dock. A gangplank would have to be set at a sharp angle in order to span between the deck and the dock. After loading, the deck surface would then drop relative to the surface of the water due to the weight of the cargo to thus become closer to the surface of the dock. Consequently, the steep gangplank angle could then be reduced.
Additionally, the natural rise and fall of the tides in the vicinity of the dock might also serve to augment the problems encountered to thus cause an even increased elevation of the deck above the surface of the dock at those times when the incidence of high tide was simultaneous with a completely evacuated hold. The present invention seeks to overcome the difficulties stemming from the great changes in deck elevation by providing an extendable safety gangplank which functions to provide an elongated, adjustable walkway which can be automatically extended, retracted, elevated or depressed in response to the increase or decrease in relative elevation of the deck of the ship above the surface of the dock.